Heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. Heat assisted magnetic recording allows for the use of small grain media, which is desirable for recording at increased areal densities, with a larger magnetic anisotropy at room temperature to assure sufficient thermal stability. By heating the medium, the material's magnetic crystalline anisotropy energy density or the coercivity is reduced such that the magnetic write field is sufficient to write to the medium. Once the medium cools to ambient temperature, the medium has a sufficiently high value of coercivity to assure thermal stability of the recorded information. Heat assisted magnetic recording is also referred to a thermally assisted magnetic recording.
In heat assisted magnetic recording, confined optical energy may be delivered to a metallic data storage medium efficiently. Near field transducers (NFT's) are used for this purpose. Based on the dominant polarization of the light in the coupling region, the near field transducers can be broadly classified as longitudinal (i.e., polarization normal to the medium) or transverse type (i.e., polarization transverse to the medium). Longitudinal NFT's show promise in terms of efficiently scaling down the area of the confined region. Typically, to excite such longitudinal NFT's, an optical condenser is used to produce a longitudinal polarization of the optical energy in the focal region.
One light delivery system uses a channel waveguide. However, the dominant electric field component in typical channel waveguide modes is transverse to the direction of propagation. These modes are incompatible with longitudinal NFT's.